An Electron Microscopy study of the BaxLa1-xFeO3-x/2 (1/2≤x≤2/3) system

1990 ◽  
Vol 48 (4) ◽  
pp. 608-609
Author(s):  
M. Parras ◽  
J.M. González-Calbet ◽  
M. Vallet-Regí ◽  
J.C. Grenier
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Chemical Analysis ◽  
Analysis Data ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Compositional Variations ◽  
Perovskite Unit Cell

In a previous paper we have shown that compositional variations in BaxLa1-xFeO3-y materials prepared in air. are accommodated in a different way than in other perovskite-related ferrites probably due to the bigger size of barium.When oxidated BaxLa1-xFe3+,4+O3-y samples in the 1/2 ≤ x ≤ 2/3 range, are reduced by annealing at 1100°C for 24h. in flowing Ar-5%H2, all iron,as deduced from chemical analysis data, is found in the III state oxidation. Powder X-ray diffraction data in this range (La1/2Ba1/2FeO2.75-La1/3Ba2/3FeO2.67) can be indexed on the basis of a single cubic perovskite unit cell (ac ≃ 3.95Å)In order to elucidate the way in which anionic vacancies are accommodated in these solids an electron diffraction (ED) and microscopy study was performed, similar results being obtained in both La1/2Ba1/2 FeO2.75 and La1/3Ba2/3FeO2.67samples.

ELECTRON MICROSCOPY STUDY OF THE SUPERCONDUCTOR “Bi2Sr2CaCu2O8+δ”

1988 ◽  
Vol 02 (01) ◽  
pp. 491-500 ◽  
Author(s):  
M. HERVIEU ◽  
C. MICHEL ◽  
B. DOMENGES ◽  
Y. LALIGANT ◽  
A. LEBAIL ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Double Perovskite ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Nominal Composition ◽  
X Ray Diffraction ◽  
Perovskite Layer ◽  
X Ray ◽  
Crystal Electron

The structural study of the superconductor Bi 2 Sr 2 CaCu 2 O 8+δ was performed by X-ray diffraction on a single crystal, electron diffraction and electron microscopy. The structure of this oxide which crystallizes in the space group Amaa, with [Formula: see text] and c≃30.7 Å can be described as an intergrowth of an oxygen deficient double perovskite layer [Sr2CaCu2O6]∞ with ( BiO y)2 layers. The E.D. patterns show the existence of satellites in incommensurate positions. The HREM images and their simulation suggest that the [BiOy]∞ layers are not [ Bi 2 O 2] Aurivillius type layers. Modulations along the a axis and much more rarely along b are observed. Stacking defects are rarely observed along c: they correspond to the intergrowth of a phase Bi 2 Sr 2 CuO 6+δ which is assumed to be the superconductor at 22K previously detected for the nominal composition “ Bi 2 Sr 2 Cu 2 O 7”.

Microdomains in BaFeO3-y (0.35 < y < 0.50)

1990 ◽  
Vol 48 (4) ◽  
pp. 780-781
Author(s):  
M. Vallet-Regí ◽  
M. Parras ◽  
J.M. González-Calbet ◽  
J.C. Grenier
Keyword(s):  
Electron Diffraction ◽  
Chemical Analysis ◽  
Monoclinic Phase ◽  
Orthorhombic Phase ◽  
Total Iron ◽  
Zone Axis ◽  
Electron Micrograph ◽  
X Ray Diffraction ◽  
X Ray ◽  
Compositional Variations

BaFeO3-y compositions (0.35<y<0.50) have been investigated by means of electron diffraction and microscopy to resolve contradictory results from powder X-ray diffraction data.The samples were obtained by annealing BaFeO2.56 for 48 h. in the temperature range from 980°C to 1050°C . Total iron and barium in the samples were determined using chemical analysis and gravimetric methods, respectively.In the BaFeO3-y system, according to the electron diffraction and microscopy results, the nonstoichiometry is accommodated in different ways as a function of the composition (y):In the domain between BaFeO2.5+δBaFeO2.54, compositional variations are accommodated through the formation of microdomains. Fig. la shows the ED pattern of the BaFeO2.52 material along thezone axis. The corresponding electron micrograph is seen in Fig. 1b. Several domains corresponding to the monoclinic BaFeO2.50 phase, intergrow with domains of the orthorhombic phase. According to that, the ED pattern of Fig. 1a, can be interpreted as formed by the superposition of three types of diffraction maxima : Very strong spots corresponding to a cubic perovskite, a set of maxima due to the superposition of three domains of the monoclinic phase along [100]m and a series of maxima corresponding to three domains corresponding to the orthorhombic phase along the [100]o.

Single-crystal X-ray diffraction and electron-microscopy study of multiple-twinned Sr3(Ru0.336,Pt0.664)CuO6

2003 ◽  
Vol 59 (2) ◽  
pp. 182-189 ◽  
Author(s):  
Karen Friese ◽  
Lorenz Kienle ◽  
Viola Duppel ◽  
Hongmei Luo ◽  
Chengtian Lin
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Single Crystal ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
X Ray Diffraction ◽  
Threefold Axis ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Twin Model

Sr_3(Ru_{0.336},Pt_{0.664})CuO_6 crystallizes as a monoclinic structure [space group R12/c; lattice parameters a = 9.595 (15), b = 9.595 (15), c = 11.193 (2) Å and \gamma = 120°]. The crystal structure is pseudotrigonal and the crystal investigated here by single-crystal X-ray diffraction was a multiple twin composed of six individuals. The twin laws are a combination of rhombohedral obverse/reverse twinning plus the threefold axis from the trigonal system. The crystal structure is related to the hexagonal perovskites. Each Pt/Ru atom is coordinated pseudo-octahedrally by O atoms, while the overall coordination polyhedra for Cu atoms can be regarded as a strongly distorted trigonal prism, where the Cu atom is clearly shifted from the center. Each [(Ru_{0.336},Pt_{0.664})O_6] octahedron is connected to two Cu—O polyhedra via a common edge, and thus chains are formed parallel to the crystallographic c axis. Sr^{2+} ions are incorporated between the chains and are coordinated by eight O atoms. All bond distances and angles are in good agreement with literature values. Electron-microscopy studies confirm the results from X-ray diffraction and all observed domain structures can be interpreted exactly with the established twin model. No indication of Pt/Ru ordering was found in either the X-ray or the electron-microscopy investigation.

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